However - I think I sanded just a bit too far on the saddle thickness (height and width are just fine), such that there is the slightest amount of play in the slot. I think there's a slight loss of volume compared to the bone and tusq - despite my strong preference for the FWI tone.

Any good ideas how to build it up just a bit? I've heard suggestions of using super glue to build up bridge pins for instance. Also, I assume building up the back side would be preferable?

Not sure if there's much point getting a high-performance saddle material and then smearing glue all over it. I'd probably just order up a couple more blanks and write that off as a useful learning experience in precision lutherie.

I think you're gonna need a new one, because the saddle is so critical to transmitting sound from string to soundboard. But as a temporary fix you could try one of these homebrew methods:

1) Brush thin coat of Z-poxy or similar epoxy/super glue on the back side of the saddle, and let it fully cure before inserting.

2) Put a thin strip of metallic tape on the back side of the saddle

3) Take one of those flat cocktail toothpicks and, after installing the saddle, try to wedge the end between the back of the saddle and the saddle cavity. Break off the excess. Start in the middle then put another little wedge on each side to keep saddle straight.

As above poster says though you really need to chalk it up to experience and grab a new blank, but maybe one of the above will help you get by in the meantime.

__________________
Silver Creek T-170
Recording King RR-50-VS
Recording King ROS-626
Martin OM28V
...and newest member of the family, the ROS-06!

yes, try to build up the back side along the bottom edge with superglue. I was told the tone transfer is primarily along the front face. But then I hate to give my opinion as so many people think I am an idiot.

A shim works OK to increase the depth of a saddle (indeed several manufacturers put shims under their saddles to allow for subsequent set up adjustments). A piece of plastic cut from an old credit card works fine - you can either just sit it in the saddle slot under the saddle or stick it to the base of the saddle with some superglue.

Another (very good) method is to use Mexican Clay. This is a self-hardening modelling clay available in most craft shops. You just roll out a thin layer (~1mm) of clay, cut out a strip the same size as the base of the saddle with a razorblade and pop it in the slot with the saddle on top. String up the guitar and leave overnight for the clay to harden. The clay forms itself to the profile of the slot base and the saddle itself so you get a perfect contact between the two.

The clay is also great if you have an electro-acoustic guitar with an under-saddle piezo transducer - a thin strip between the base of the slot and the transducer and also the transducer and the saddle ensures a perfect contact and improves the amplified sound.

I think you will find super glue will work fine. Try to get it on as even as possible - the gel version will probably work better unless your gap is extremely narrow. Then sand it to fit. I have done it & noticed no loss of sound.

A shim works OK to increase the depth of a saddle (indeed several manufacturers put shims under their saddles to allow for subsequent set up adjustments). A piece of plastic cut from an old credit card works fine - you can either just sit it in the saddle slot under the saddle or stick it to the base of the saddle with some superglue....

If i am not wrong he said the saddle is not too talll but too thin, so shimming it on the bottom is not what he needs.
Anyway, if the saddle is not merely a "piece of something" laying between the bridge and the strings, and if putting a precious FWI saddle was intended to enrich the sound and the sustain, it sounds absurd tho put a shim of *plastic*
or a layer of glue under or aside it

Well, I did it last night with brushed on Krazy glue. It all worked fine. Just had to be patient while it dried. Tone sounds the same as it did beforehand, but at least now it should be more stable structurally.

It really was only the slightest wiggle beyond normal tolerance, and I think the fix worked fine. Someday I'll probably get a new one, but I think I'm good for now.